„Roughly 16% of Uber rides are tipped,“ the study’s authors wrote. „Yet, most riders (60%) never tip over our four weeks of data collection. Of those who do tip, very few (1%) tip on every trip. The remainder of people only tip on about 25% of trips.“

Perhaps unsurprisingly, highly rated drivers made more in tips than those with fewer stars, but those amounts began to slide even with averages that many would likely consider to still be premium.

When it comes to gender, female drivers also get tipped a premium, but only up to a certain age, the researchers found.

„Further, female drivers are tipped more than male drivers — a fact that is true regardless of rider gender: men (women) tip female drivers nearly 12% (11%) more than they tip male drivers,“ the researchers wrote. „However, the tip premium that male riders pay to female drivers falls with the driver’s age and disappears by the age of 65. This tipping difference results in a $0.05 per trip driver gender tip gap.“

„In terms of magnitudes, drivers with a 5-star rating are tipped close to 50% more often than those with a 4.75 rating,“ the authors said, „and when they do receive tips they are nearly 5% higher.“

And that works both ways.

„Rider ratings represent a key demand-side explanatory variable,“ researchers said. „We find that, for example, riders who have a 5-star rating tip more than twice as often as those with a 4.75 rating, and when they do tip they tip nearly 14% more.“

Many of the paper’s findings may help to codify anecdotes drivers have told Business Insider for months.

„Most people don’t tip,“ Jenny, a driver in New Jersey who requested anonymity in order to speak candidly about her work driving for Uber and Lyft, told Business Insider earlier this year. „I’ve found people are more likely to tip if I have a conversation, and I seem to get more from service workers, or people on business trips who can expense the tip.“

The researchers found data to back up her theory, too, saying that „tips tend to be highest for airport and business trips.“

Michael, a driver in Dallas, estimated earlier this year that roughly 10% of his passengers left tips.

„Most people don’t even tip,“ he said bluntly. „Some people will say they’re going to tip on the app, but then don’t.“

„Most people would not even bat an eye at tipping any people in these professions,“ he writes of waiters, bellhops, and other jobs where tipping is expected. „But somehow, Uber and Lyft drivers became exempt from this group.“

An Uber representative cautioned that the data set used for the study, while massive, was limited to 2017 data. The representative offered no examples of significant changes to Uber’s tipping policy or app interface that might affect how riders tip. Notably, Uber only added a tipping function to its app in 2017, after an outpouring of requests from both riders and drivers.

„In just over two years, drivers on Uber and delivery partners on Uber Eats have received nearly $2 billion in tips — on top of their earnings,“ the representative said in an email. „This feature remains one of the most popular among riders, drivers, and delivery partners. We’re committed to developing and improving features that help detect and mitigate bias on our platform.“